Drilling fluids used in the drilling of subterranean oil and gas wells as well as other drilling fluid applications and drilling procedures are known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply "muds". The drilling fluid is expected to carry cuttings up from beneath the bit, transport them up the annulus, and allow their separation at the surface while at the same time the rotary bit is cooled and cleaned. A drilling mud is also intended to reduce friction between the drill string and the sides of the hole while maintaining the stability of uncased sections of the borehole. The drilling fluid is formulated to prevent unwanted influxes of formation fluids from permeable rocks penetrated and also often to form a thin, low permeability filter cake which temporarily seals pores, other openings and formations penetrated by the bit. The drilling fluid may also be used to collect and interpret information available from drill cuttings, cores and electrical logs. It will be appreciated that within the scope of the claimed invention herein, the term "drilling fluid" also encompasses "drill-in fluids" and "completion fluids".
Drilling fluids are typically classified according to their base material. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water. Nonetheless, the water is the continuous phase. Oil-based muds are the opposite. Solid particles are suspended in oil, and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds which are water-in-oil emulsions are also called invert emulsions. Brine-based drilling fluids, of course are a water-based mud in which the aqueous component is brine.
Special problems occur when drilling into certain formation types, such as shale which contain clays. Clay particles will hydrate (absorb water) and interfere with drilling operations by causing bit balling and other problems. It is thus customary when using aqueous-based drilling fluids in dispersive shale formations to include a clay stabilizer additive (or shale stabilizer) to control clay hydration and disintegration during drilling. The clay stabilizer additive is to inhibit the dispersion and wetting, and thus swelling tendencies, of drilled clay particles. Ideally the clay stabilizer additive coats the drilled particles immediately after they are drilled to inhibit water from penetrating and swelling the clays within the shale. Clay stabilizer additives also aid in friction reduction and improving lubricity.
However, clay stabilizers are like many drilling fluid additives in that they are relatively expensive. It would be desirable to be able to determine how much clay stabilizer is present within a drilling mud so that there is enough present to be effective, but not so much that excessive amounts are being wasted. The same considerations would be true for other additives to drilling, drill-in, and completion fluids which would include corrosion inhibitors, surfactants, and the like.
In general, it is apparent to those selecting or using a drilling fluid for oil and/or gas exploration that an essential component of a selected fluid is that it be properly balanced to achieve all of the necessary characteristics for the specific end application. Because the drilling fluids are called upon to do a number of tasks simultaneously, this desirable balance is not always easy to accomplish, nor is it easy to achieve in the most economical fashion possible.
It would be desirable if compositions and methods could be devised to aid and improve the ability of drilling fluids to simultaneously accomplish these tasks.